Binder for battery, and anode and lithium battery including the same

ABSTRACT

A binder for a battery including polymethyl methacrylate particles and a binder polymer is disclosed. Additionally, a binder composition, and an anode and a lithium battery which include the binder are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

Any and all priority claims identified in the Application Data Sheet, orany correction thereto, are hereby incorporated by reference under 37CFR 1.57. For example, this application claims the benefit of KoreanPatent Application No. 10-2013-0018254, filed on Feb. 20, 2013, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND

1. Field

The present invention relate to a binder for a battery, and an anode anda lithium battery including the same.

2. Description of the Related Technology

Lithium batteries are used in various applications due to their highvoltage and high energy density characteristics. For example, in thefield of electric vehicles such as hybrid electric vehicles (HEVs) andplug-in hybrid electric vehicles (PHEVs), because the battery isrequired to operate at a high temperature, provide a large amount ofelectricity during charge or discharge, and have a prolonged operationtime. A lithium battery having excellent discharge capacity and lifecharacteristics is needed meet these requirements.

The carbon-based material is porous and is stable because of its smallvolume change during charging and discharging. However, the capacity ofthe battery using the carbon-based material is generally low due to theporous structure of carbon. For example, the theoretical capacity ofgraphite having high crystallinity is about 372 mAh/g for a LiC₆composition.

The metal alloyable with lithium may be used as an anode active materialhaving a high capacity in comparison to the carbon-based material.Examples of metals alloyable with lithium include silicon (Si), tin(Sn), aluminum (Al), etc. However, the metals alloyable with lithium caneasily deteriorate and have short battery life. For example, in the caseof Sn, Sn particles are electrically isolated by repeated aggregationand crushing processes during the repeated charge and discharge.

Therefore, a binder, which may increase the battery life characteristicsof a lithium battery by accommodating and/or inhibiting the volumechange of the above non-carbon-based anode active material, is indemand.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One aspect of the present disclosure relates to a binder for a batterywhich has increased strength.

One or more embodiments of the present disclosure include a bindercomposition for a battery.

One or more embodiments of the present invention include an anodeincluding the binder.

One or more embodiments of the present invention include a lithiumbattery using the anode, wherein the anode contains the binder describedherein.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

One aspect of the present disclosure relates to a binder for a battery,the binder comprising polymethyl methacrylate particles; and a binderpolymer.

In some embodiments, an average particle diameter of the polymethylmethacrylate particles is in the range of about 10 nm to about 200 nm.

In some embodiments, the weight ratio of the polymethyl methacrylateparticles to the binder polymer is in the range of about 100:10 to about100:60.

In some embodiments, the binder for the battery has one or more glasstransition temperatures.

In some embodiments, the binder for the battery has one or more glasstransition temperatures of about 60° C. or less.

In some embodiments, the glass transition temperature of the binder forthe battery is in the range of about −50° C. to about 60° C.

In some embodiments, the polymethyl methacrylate particles in the binderfor the battery are crosslinked polymethyl methacrylate particles thatdo not have a glass transition temperature.

In some embodiments, the binder further comprises a coupling agent.

In some embodiments, the coupling agent is a silane-based compound.

In some embodiments, the coupling agent is a hydrolysate of a silanecoupling agent.

In some embodiments, the silane coupling agent comprises one or moreselected from the group consisting of an alkoxy group, a halogen group,an amino group, a vinyl group, a glycidoxy group, and a hydroxyl group.

In some embodiments, the silane coupling agent comprises one or moreselected from the group consisting of vinylalkylalkoxysilane,epoxyalkylalkoxysilane, mercaptoalkylalkoxysilane, vinylhalosilane, andalkylacyloxysilane.

An additional aspect of the present disclosure relates to a bindercomposition for a battery comprising: polymethyl methacrylate particles;binder polymer particles; and a solvent.

In some embodiments, the polymethyl methacrylate particles are includedin an amount of about 10 parts by weight to about 60 parts by weightbased on 100 parts by weight of the binder polymer particles.

In some embodiments, an average particle diameter of the polymethylmethacrylate particles is in the range of about 10 nm to about 200 nm.

In some embodiments, an average particle diameter of the binder polymerparticles is in the range of about 50 nm to about 500 nm.

One more aspect of the present disclosure relates to an anodecomprising: an anode active material; and the binder for the battery ofany one of claim 1.

In some embodiments, the binder for the battery in which polymethylmethacrylate particles are dispersed.

In some embodiments, the anode active material comprises one or moreselected from the group consisting of silicon (Si), tin (Sn), lead (Pb),germanium (Ge), aluminum (Al), SiOx (0<x≦2), SnOy (0<y≦2), Li4Ti5O12,TiO2, LiTiO3, and Li2Ti3O7.

In some embodiments, the anode active material further comprises acarbon-based anode active material.

One more aspect of the present disclosure relates to a lithium batteryusing the anode described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a lithium battery according to anexemplary embodiment.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Hereinafter, a binder for a battery, a binder composition, an anodeincluding the binder, and a lithium battery using the anode aredescribed in more detail.

In some embodiments, a binder for a battery may include polymethylmethacrylate particles and a binder polymer. Since the binder for thebattery may have high strength by including the polymethyl methacrylateparticles, the binder for the battery may accommodate and/or inhibit thevolume change of an anode active material during charge and discharge.Thus, the cycle characteristics of a lithium battery including thebinder may be improved.

In particular, the binder for a battery may maintain a high elasticmodulus by including the polymethyl methacrylate particles at a hightemperature of about 50° C. or more. In particular, the binder for abattery may maintain a high elastic modulus at a high temperature ofabout 60° C. or more. The binder for a battery is substantially in thestate of having no solvent, in which the binder polymer does not haveany particular form and may act as a kind of a matrix.

The average particle diameter of the polymethyl methacrylate particlesin the binder may be in the range of about 10 nm to about 200 nm. Forexample, the average particle diameter of the polymethyl methacrylateparticles may be in the range of about 10 nm to about 100 nm. Forexample, the average particle diameter of the polymethyl methacrylateparticles may be in the range of about 20 nm to about 100 nm. When theaverage particle diameter of the polymethyl methacrylate particles isexcessively small, preparation may become difficult. When the averageparticle diameter of the polymethyl methacrylate particles isexcessively large, the strength of the binder may be reduced.

The polymethyl methacrylate particles may have a polar functional groupon the surfaces thereof. The polar functional group may form variousbonds, such as hydrogen bond and covalent bond, with the binder polymer.For example, the polar functional group may be a carboxylic group or ahydroxyl group. However, the polar functional group is not limitedthereto, and any polar functional group may be used so long as it mayform a bond with the binder polymer.

The binder polymer may have a polar functional group on at least aportion of the main chain and/or the side chain. The polar functionalgroup may form various bonds, such as hydrogen bond and covalent bondswith the polymethyl methacrylate particles. The polar functional groupmay be a carboxylic group or a hydroxyl group. However, the polarfunctional group is not limited thereto, and any polar functional groupmay be used so long as it may form a bond with the polymethylmethacrylate particles.

In some embodiments, the polymethyl methacrylate particles and thebinder polymer may form a composite. That is, the polymethylmethacrylate particles and the binder polymer may further include achemical bond which is formed by reacting the polar functional group onthe surfaces of the polymethyl methacrylate particles and the polarfunctional group at the end of the binder polymer together, in additionto a physical bond such as a van der Waals bond.

In some embodiments, the weight ratio of the polymethyl methacrylateparticles to the binder polymer in the binder may be in the range ofabout 100:1 to about 100:60. In some embodiments, based on the dryweight, the binder may include the polymethyl methacrylate particles inan amount of about 1 part by weight to about 60 parts by weight based on100 parts by weight of the binder polymer. In some embodiments, based onthe dry weight, the binder may include the polymethyl methacrylateparticles in an amount of about 5 parts by weight to about 60 parts byweight based on 100 parts by weight of the binder polymer. In someembodiments, based on the dry weight, the binder may include thepolymethyl methacrylate particles in an amount of about 10 parts byweight to about 60 parts by weight based on 100 parts by weight of thebinder polymer. When the amount of the polymethyl methacrylate particlesis excessively low, the elasticity of the binder may be reduced. Whenthe amount of the polymethyl methacrylate particles is excessively high,the addition of the electrolyte solution may be difficult.

The binder for a battery may have one or more glass transitiontemperatures. In some embodiments, the binder for a battery may have asingle glass transition temperature. In some embodiments, the binder fora battery may have two glass transition temperatures.

The binder for a battery may have one or more glass transitiontemperatures of about 60° C. or less. In some embodiments, the binderfor a battery may have one or more glass transition temperatures ofabout 50° C. or less. In some embodiments, the binder for a battery mayhave one or more glass transition temperatures of about 40° C. or less.

The glass transition temperature of the binder for a battery may be inthe range of about −50° C. to about 60° C. In some embodiments, theglass transition temperature of the binder for a battery may be in therange of about −40° C. to about 50° C. In some embodiments, the glasstransition temperature of the binder for a battery may be in the rangeof about −30° C. to about 40° C.

The polymethyl methacrylate particles in the binder for a battery may becrosslinked polymethyl methacrylate particles that do not have a glasstransition temperature. The crosslinked polymethyl methacrylateparticles are not particularly limited and may be prepared by variousmethods such as emulsion polymerization and solution polymerization.Also, reaction conditions used in the above methods may be appropriatelycontrolled by a person skilled in the art. The crosslinked polymethylmethacrylate particles may be prepared in the form of an aqueousdispersion having a solid content of about 15% or less.

In some embodiments, the binder polymer may include one or more selectedfrom the group consisting of a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an acrylonitrile-butadiene rubber, anacrylonitrile-butadiene-styrene rubber, an acrylic rubber, a butylrubber, a fluorine rubber, polytetrafluoroethylene, polyethylene,polypropylene, an ethylene-propylene copolymer, polyethylene oxide,polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene,polyacrylate, polyacrylonitrile, polystyrene, anethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonatedpolyethylene, latex, a polyester resin, an acrylic resin, a phenolicresin, an epoxy resin, polyvinyl alcohol, carboxymethyl cellulose,hydroxypropyl methyl cellulose, hydroxypropyl cellulose, and diacetylcellulose. However, the binder polymer is not limited thereto, and anybinder polymer may be used so long as it may be used as an aqueousbinder in the art.

Examples of a monomer used for preparing the binder polymer may be anethylenically unsaturated carboxylic acid alkyl ester such as methylmethacrylate, butyl methacrylate, ethyl methacrylate, and 2-ethylhexylmethacrylate; a cyano group-containing ethylenically unsaturated monomersuch as acrylonitrile, methacrylonitrile, α-chloro-acrylonitrile,α-cyanoethyl acrylonitrile; a conjugated diene monomer such as1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene; an ethylenicallyunsaturated carboxylic acid, such as acrylic acid, methacrylic acid,maleic acid, fumaric acid, and citraconic acid, and a salt thereof; anaromatic vinyl monomer such as styrene, alkylstyrene, and vinylnaphthalene; a fluoroalkyl vinylether such as fluoroethyl vinylether;vinylpyridine; a non-conjugated diene monomer such as vinylnorbornene,dicyclopentadiene, and 1,4-hexadiene; an α-olefin such as ethylene andpropylene; an ethylenically unsaturated amide monomer such asmethacrylamide. However, the monomer is not necessarily limited to theabove, and any suitable monomer may be used as long.

The binder polymer is not particularly limited and may be prepared byvarious methods such as emulsion polymerization and solutionpolymerization. Also, reaction conditions used in the above methods maybe appropriately controlled by a person skilled in the art.

The binder may further include a coupling agent. The coupling agent maybe a silane-based compound. The coupling agent may be a hydrolysate of asilane coupling agent.

In some embodiments, the silane coupling agent may be a silane-basedcompound having a hydrolytic functional group. The hydrolytic functionalgroup is a functional group that may be bonded to the methylmethacrylate particles and the binder polymer after hydrolysis. Forexample, the silane coupling agent may include one or more selected fromthe group consisting of an alkoxy group, a halogen group, an aminogroup, a vinyl group, a glycidoxy group, an acyloxy group, and ahydroxyl group.

In some embodiments, the silane coupling agent may include one or moreselected from the group consisting of vinylalkylalkoxysilane,epoxyalkylalkoxysilane, mercaptoalkylalkoxysilane, vinylhalosilane, andalkylacyloxysilane.

In some embodiments, the silane coupling agent may include one selectedfrom the group consisting of vinyltris(β-methoxyethoxy)silane,γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane, γ-aminopropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane,vinyltrichlorosilane, and methyltriacetoxysilane. However, the silanecoupling agent is not necessarily limited thereto, and any silanecoupling agent may be used as long as it is used in the art.

In some embodiments, based on the dry weight, the amount of the couplingagent used in the preparation of the binder may be about 10 wt % or lessbased on the total weight of reactants. In some embodiments, based onthe dry weight, the amount of the coupling agent used in the preparationof the binder may be about 5 wt % or less based on the total weight ofthe reactants. In some embodiments, based on the dry weight, the amountof the coupling agent used in the preparation of the binder may be about3 wt % or less based on the total weight of the reactants.

The binder composition for a battery may include polymethyl methacrylateparticles; binder polymer particles; and a solvent. In the bindercomposition, the polymethyl methacrylate particles and the binderpolymer particles may be in the state of being dispersed in the solventwhile maintaining the particle shape. The polymethyl methacrylateparticles may be crosslinked polymethyl methacrylate particles. In someembodiments, the binder composition may be in the state of an emulsion.The binder composition may have a pH level of about 7 to about 11 inorder to maintain stability. Ammonia and hydroxides of alkali metals maybe used as a pH adjuster. When particle diameters of the polymethylmethacrylate particles and the binder polymer particles, which aredispersed in the binder composition, are excessively small, handling maynot be easy due to high viscosity of the emulsion. When the particlediameters of the polymethyl methacrylate particles and the binderpolymer particles, which are dispersed in the binder composition, areexcessively large, initial adhesion may be reduced.

The binder composition may include the polymethyl methacrylate particlesin an amount of about 1 part by weight to about 60 parts by weight basedon 100 parts by weight of the binder polymer particles. For example,based on the dry weight, the binder composition may include thepolymethyl methacrylate particles in an amount of about 5 parts byweight to about 60 parts by weight based on 100 parts by weight of thebinder polymer. For example, based on the dry weight, the bindercomposition may include the polymethyl methacrylate particles in anamount of about 10 parts by weight to about 60 parts by weight based on100 parts by weight of the binder polymer. When the amount of thepolymethyl methacrylate particles is excessively low, elasticity of thebinder may be reduced. When the amount of the polymethyl methacrylateparticles is excessively high, a binder, which is prepared from thebinder composition, may be difficult to dissolve in an electrolytesolution.

The average particle diameter of the polymethyl methacrylate particlesin the binder composition may be in the range of about 10 nm to about200 nm. In some embodiments, the average particle diameter of thepolymethyl methacrylate particles may be in the range of about 10 nm toabout 100 nm. In some embodiments, the average particle diameter of thepolymethyl methacrylate particles may be in the range of about 20 nm toabout 100 nm. When the average particle diameter of the polymethylmethacrylate particles is excessively small, preparation may not befacilitated. When the average particle diameter of the polymethylmethacrylate particles is excessively large, the strength of the bindermay be reduced.

The average particle diameter of the binder polymer particles in thebinder composition may be in the range of about 50 nm to about 500 nm.For example, the average particle diameter of the binder polymerparticles may be in the range of about 60 nm to about 400 nm. In someembodiments, the average particle diameter of the binder polymerparticles may be in the range of about 70 nm to about 300 nm. In someembodiments, the average particle diameter of the binder polymerparticles may be in the range of about 80 nm to about 200 nm. Thestrength and elastic modulus of the binder, which is obtained from thebinder composition, may be increased within the above average particlediameter range of the binder polymer.

The binder composition may further include a coupling agent. Thecoupling agent may form covalent bonds by reacting with polar functionalgroups that exist on the surfaces of the polymethyl methacrylateparticles and/or the binder polymer particles. In some embodiments, thepolymethyl methacrylate particles and the binder polymer particles maybe more strongly bound together by the coupling agent. The couplingagent used in the binder composition may be the same as the couplingagent used in the above-described binder.

In some embodiments, the binder composition may include the couplingagent in an amount ranging from greater than 0 to about 10 parts byweight based on 100 parts by weight of the binder polymer particles. Insome embodiments, the binder composition may include the binder polymerparticles in an amount ranging from greater than 0 to about 5 partsbased on a dry weight basis. In some embodiments, based on the dryweight, the binder composition may include the polymethyl methacrylateparticles in an amount greater than 0 to about 3 parts by weight basedon 100 parts by weight of the binder polymer particles.

In some embodiments, based on a dry weight, about 10 parts by weight toabout 50 parts by weight of the polymethyl methacrylate particles may bemixed with about 0.01 parts by weight to about 5 parts by weight of thecoupling agent based on 100 parts by weight of the binder polymerparticles in the binder composition. In some embodiments, based on a dryweight, about 10 parts by weight to about 40 parts by weight of thepolymethyl methacrylate particles may be mixed with about 0.01 parts byweight to about 3 parts by weight of the coupling agent based on 100parts by weight of the binder polymer particles.

In some embodiments, the anode may include an anode active material andthe above-described binder for a battery.

The anode may include the binder for a battery in which polymethylmethacrylate particles are dispersed. A binder polymer may act as amatrix in the binder for a battery that is included in the anode, andthe binder for a battery may have a form in which the polymethylmethacrylate particles are dispersed in the matrix. The bindercomposition is added to an electrode active material slurry, and thebinder is then formed from the binder composition in the process ofpreparing an anode by removing the solvent from the slurry.

In some embodiments, the anode may be prepared by a method in which ananode active material composition including the anode active materialand the binder for a battery is formed in a certain shape or the anodeactive material composition is coated on a current collector such as acopper foil and the like.

Specifically, an anode active material composition, in which the anodeactive material, a conductive agent, the binder, and a solvent are mixedtogether, is prepared. An anode plate is prepared by directly coatingthe anode active material composition on a metal current collector.Alternatively, the anode active material composition is cast on aseparate support, and then an anode plate may be prepared by laminatingfilms detached from the support on a metal current collector. The anodeis not limited to the foregoing shapes and may have a shape other thanthe foregoing shapes.

The anode active material may be a non-carbon-based material. Forexample, the anode active material may include one or more selected fromthe group consisting of a metal alloyable with lithium, an alloy of themetal alloyable with lithium, an oxide of the metal alloyable withlithium, transition metal oxide, and non-transition metal oxide.

Examples of the metal alloyable with lithium may include, but are notlimited to, silicon (Si), tin (Sn), aluminum (Al), germanium (Ge), lead(Pb), bismuth (Bi), antimony (Sb), an Si—Y alloy (where Y is alkalinemetal, alkaline earth metal, a group 13 to 16 element, transition metal,a rare earth element, or a combined element thereof, and provided thatthe metal alloyable is not Si), an Sn—Y alloy (where Y is alkalinemetal, alkaline earth metal, a group 13 to 16 element, transition metal,a rare earth element, or a combined element thereof, and is not Sn),etc. Examples of the element Y may be magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), radium (Ra), scandium (Sc), yttrium (Y),titanium (Ti), zirconium (Zr), hafnium (Hf), rutherfordium (Rf),vanadium (V), niobium (Nb), tantalum (Ta), dubnium (Db), chromium (Cr),molybdenum (Mo), tungsten (W), seaborgium (Sg), technetium (Tc), rhenium(Re), bohrium (Bh), iron (Fe), Pb, ruthenium (Ru), osmium (Os), hassium(Hs), rhodium (Rh), iridium (Ir), palladium (Pd), platinum (Pt), copper(Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), boron (B), Al,gallium (Ga), Sn (Tin), indium (In), Ge, phosphorus (P), arsenic (As),Sb (Antimony), Bi (Bismuth), sulfur (S), selenium (Se), tellurium (Te),polonium (Po), and combinations thereof.

In some embodiments, the transition metal oxide may be lithium titanate,vanadium oxide, lithium vanadium oxide, etc.

In some embodiments, the non-transition metal oxide may be SnO₂, SiO_(x)(0<x<2), etc.

Specifically, the anode active material may include one or more selectedfrom the group consisting of Si, Sn, Pb, Ge, Al, SiO_(x) (0<x≦2),SnO_(y) (0<y≦2), Li₄Ti₅O₁₂, TiO₂, LiTiO₃, and Li₂Ti₃O₇. However, theanode active material is not necessarily limited thereto, and any anodeactive material may be used so long as it is used as a non-carbon-basedanode active material in the art.

In some embodiments, the composition of a non-carbon-based anode activematerial and a carbon-based material may be used, and a carbon-basedanode active material may be further included in addition to thenon-carbon-based material.

The carbon-based material may include crystalline carbon, amorphouscarbon, or a mixture thereof. The crystalline carbon may be graphitesuch as amorphous, plate, flake, spherical, or fibrous natural graphiteor artificial graphite. In some embodiments, the amorphous carbon may besoft carbon (low-temperature fired carbon) or hard carbon, mesophasepitch carbide, fired coke, etc.

Examples of the conductive agent may be acetylene black, Ketjen black,natural graphite, artificial graphite, carbon black, acetylene black,carbon fibers, metal powders such as copper, nickel, aluminum, orsilver, metal fibers, etc. Also, the conductive agent may be used bymixing one or more conductive materials such as a polyphenylenederivative. However, the conductive agent is not limited thereto and anyconductive agent known in the art may be used. Further, theabove-described crystalline carbon-based material may be included as aconductive agent.

In some embodiments, a typical binder may further be used in addition tothe above binder. Examples of a typical binder may be vinylidenefluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF),polyacrylonitrile, poly(methyl methacrylate), polytetrafluoroethylene,and mixtures thereof. In some embodiments, a typical binder can also bea styrene butadiene rubber-based polymer. However, the binder is notlimited thereto and any binder known in the art may be used.

Examples of a solvent may be N-methylpyrrolidone, acetone, water, etc.However, the solvent is not limited thereto and any solvent may be usedas long as it is known in the art.

The amount of the anode active material, conductive agent, typicalbinder, and solvent are based on the typical amounts used in a lithiumbattery. One or more of the conductive agent, typical binder, andsolvent may be omitted according to applications and configurations ofthe lithium batteries.

In some embodiments, the lithium battery may use the anode describedherein. The lithium battery may be prepared according to the followingmethod.

First, an anode is prepared according to a method of preparing the anodethat is known in the art.

Next, a cathode active material composition, in which a cathode activematerial, a conductive agent, a binder and a solvent are mixed together,is prepared. The cathode active material composition is directly coatedon a metal current collector and dried to prepare a cathode plate.Alternatively, the cathode active material composition is cast on aseparate support and then a cathode plate may be prepared by laminatingfilms detached from the support on a metal current collector.

The cathode active material may include one or more materials selectedfrom the group consisting of lithium cobalt oxide, lithium nickel cobaltmanganese oxide, lithium nickel cobalt aluminum oxide, lithium ironphosphate, lithium manganese oxide, and combinations thereof. However,the cathode active material is not limited thereto and any cathodeactive material may be used as long as it is known in the art.

For example, a compound expressed as one of the following chemicalformulas may be used: Li_(a)A_(1-b)B_(b)D₂ (where 0.90≦a≦1.8, 0≦b≦0.5);Li_(a)E_(1-b)B_(b)O_(2-c)D_(c) (where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);LiE_(2-b)B_(b)O_(4-c)D_(c) (where 0≦b≦0.5, 0≦c≦0.05);Li_(a)Ni_(1-b-c)Co_(b)B_(c)D_(α) (where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05,0<α≦2); Li_(a)Ni_(1-b-c)Co_(b)B_(c)O_(2-α)F_(α) (where 0.90≦a≦1.8,0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li_(a)Ni_(1-b-c)Co_(b)B_(c)O_(2-α)F₂ (where0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)B_(c)D¹_(α) (where 0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α≦2);Li_(a)Ni_(1-b-c)Mn_(b)B_(c)O_(2-α)F_(α) (where 0.90≦a≦1.8, 0≦b≦0.5,0≦c≦0.05, 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)B_(c)O_(2-α)F¹ ₂ (where0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂ (where0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂(where 0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1);Li_(a)NiG_(b)O₂ (where 0.90≦a≦1.8, 0.001≦b≦0.1); Li_(a)CoG_(b)O₂ (where0.90≦a≦1.8, 0.001≦b≦0.1); Li_(a)MnG_(b)O₂ (where 0.90≦a≦1.8,0.001≦b≦0.1); Li_(a)Mn₂G_(b)O₄ (where 0.90≦a≦1.8, 0.001≦b≦0.1); QO₂;QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiI¹O₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≦f≦2);Li_((3-f))Fe₂(PO₄)₃ (0≦f≦2); and LiFePO₄.

In the above chemical formulas, A is nickel (Ni), cobalt (Co), manganese(Mn), or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V,rare earth elements, or a combination thereof; D¹ is oxygen (O),fluorine (F), S, P, or a combination thereof; E is Co, Mn, or acombination thereof; F¹ is F, S, P, or a combination thereof; G is Al,Cr, Mn, Fe, Mg, lanthanum (La), cerium (Ce), Sr, V, or a combinationthereof; Q is Ti, Mo, Mn, or a combination thereof; I¹ is Cr, V, Fe, Sc,Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or acombination thereof.

In some embodiments, a compound having a coating layer on the foregoingcompounds may be used. In some embodiments, a composition may be used bymixing the foregoing compounds and the compound having a coating layer.The coating layer may include a compound of a coating element such asoxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of acoating element. The compound constituting the coating layer may beamorphous or crystalline. Examples of the coating element included inthe coating layer may be Mg, Al, Co, potassium (K), sodium (Na), Ca, Si,Ti, V, Sn, Ge, Ga, B, As, Zr, and mixtures thereof. Any coating methodmay be used for a process of forming a coating layer as long as coatingmay be performed by a method (e.g., spray coating, dipping, etc.) thatdoes not adversely affect the physical properties of the cathode activematerial due to using such coating elements on the foregoing compounds.Detailed description related to the coating method is not providedbecause it is obvious to those skilled in the art.

Examples of the cathode active material may be LiNiO₂, LiCoO₂,LiMn_(x)O_(2x) (x=1, 2), LiNi_(1-x)Mn_(x)O₂ (0<x<1),LiNi_(1-x-y)Co_(x)Mn_(y)O₂ (0≦x≦0.5, 0≦y≦0.5); LiFeO₂, V₂O₅, TiS, MoS,etc.

The conductive agent, binder, and solvent in the cathode active materialcomposition may be used the same as those in the anode active materialcomposition. Pores may be formed within an electrode plate by furtheradding a plasticizer to the cathode active material composition and/oranode active material composition.

The amounts of the cathode active material, conductive agent, typicalbinder, and solvent are amounts typically used in a lithium battery. Oneor more of the conductive agent, typical binder, and solvent may beomitted according to applications and configurations of lithiumbatteries.

Next, a separator, which will be inserted between the cathode and theanode, is prepared. Any separator that is typically used in a lithiumbattery may be used as the separator. A separator having highmoisture-retention ability for an electrolyte as well as low resistanceto the transfer of electrolyte ions may be used. Examples of theseparator may be one selected from the group consisting of glass fibers,polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene(PTFE), and combinations thereof. The separator may be a nonwoven orwoven fabric type. For example, a windable separator such aspolyethylene or polypropylene is used in a lithium-ion battery, and aseparator having high moisture-retention ability for an organicelectrolyte may be used in a lithium-ion polymer battery. For example,the separator may be prepared according to the following method.

In some embodiments, the separator composition is prepared by mixing apolymer resin, a filler, and a solvent. The separator composition isdirectly coated on an upper portion of an electrode and dried to preparea separator. Also, the separator composition is cast and dried on asupport, and then a separator may be prepared by laminating separatorfilms detached from the support on an upper portion of an electrode.

A polymer resin used in the preparation of the separator is notparticularly limited thereto and any material used in the binder for anelectrode plate may be used. Examples of the polymer resin may bevinylidene fluoride/hexafluoropropylene copolymer, PVDF,polyacrylonitrile, poly(methyl methacrylate), and mixtures thereof.

Next, an electrolyte is prepared.

In some embodiments, the electrolyte may be an organic electrolyte. Insome embodiments, the electrolyte may be a solid. For example, theelectrolyte may be boron oxide, lithium oxynitride, etc. However, theelectrolyte is not limited thereto and any electrolyte may be used solong as it may be used as a solid electrolyte in the art. The solidelectrolyte may be formed on the anode by using a method such assputtering.

In some embodiments, an organic electrolyte may be prepared. The organicelectrolyte may be prepared by dissolving a lithium salt in an organicsolvent.

Any suitable organic solvent known in the art may be used as long as itis. Examples of the organic solvent may be propylene carbonate, ethylenecarbonate, fluoroethylene carbonate, butylene carbonate, dimethylcarbonate, diethyl carbonate, methylethyl carbonate, methylpropylcarbonate, ethylpropyl carbonate, methylisopropyl carbonate, dipropylcarbonate, dibutyl carbonate, benzonitrile, acetonitrile,tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane,4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide,dimethylsulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane,dichloroethane, chlorobenzene, nitrobenzene, diethyleneglycol,dimethylether, and mixtures thereof.

Any suitable lithium salt known in the art may be used. Examples of thelithium salt may be LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄, LiCF₃SO₃,Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiAlO₂, LiAlCl₄, LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (where x and y are natural numbers), LiCl, LiI, andmixtures thereof.

As shown in FIG. 1, a lithium battery 1 includes a cathode 3, an anode2, and a separator 4. The cathode 3, anode 2, and separator 4 are woundand folded to be enclosed in a battery case 5. Subsequently, an organicelectrolyte solution is injected into the battery case 5 and the lithiumbattery 1 is completed by being sealed with a cap assembly 6. Thebattery case 5 may be a cylindrical, rectangular, or thin-film type. Forexample, the lithium battery 1 may be a thin-film type battery. Thelithium battery 1 may be a lithium-ion battery.

A separator is disposed between the cathode and the anode such that abattery structure may be formed. The battery structure is stacked in abi-cell structure, and then combined with an organic electrolytesolution. A lithium-ion polymer battery is completed when the resultedproduct is contained in a pouch and sealed.

Also, battery structures are stacked to form a battery pack, and thebattery pack may be used in all devices requiring high capacity and highpower. For example, the battery pack may be used in a notebook,smartphone, or electric vehicle (EV).

Particularly, because the lithium battery has excellent high-rate andlife characteristics, it is appropriate for an EV. For example, thelithium battery is appropriate for a hybrid vehicle (HV) such as aplug-in hybrid electric vehicle (PHEV).

The present invention is described in more detail according to examplesand comparative examples below. However, examples only exemplify thepresent invention, and the scope of the present invention is not limitedthereto.

Preparation of First Polymer Emulsion PREPARATION EXAMPLE 1

After flushing nitrogen in a flask reactor equipped with a condenser, athermometer, a monomer emulsion inlet tube, a nitrogen gas inlet tube,and a stirrer, about 60 parts by weight of distilled water and about 1.5parts by weight of dodecylbenzenesulfonic acid sodium salt were added,and the temperature was increased to about 80° C. Subsequently, about 2parts by weight of styrene was added to the reactor and stirred forabout 5 minutes. Then, about 10 parts by weight of a 5% aqueous solutionof ammonium persulfate was added to the reactor to initiate a reaction.After about 1 hour, a monomer emulsion, which included about 30 parts byweight of 2-ethylhexyl acrylate, about 68 parts by weight of styrene,about 2 parts by weight of acrylic acid, about 0.5 parts by weight of adodecylbenzenesulfonic acid sodium salt, and about 40 parts by weight ofdistilled water, was dropped into the reactor for about 3 hours.Simultaneously, about 6 parts by weight of the 5% aqueous solution ofammonium persulfate was dropped into the reactor for about 3 hours.After finishing the addition of the monomer emulsion, the reaction wasthen further performed for about 2 hours. Then, the reactor were cooledto 20° C., a 5 wt % lithium hydroxide aqueous solution was added intothe reactor to adjust the pH level to about 8.5, the residual monomerwas removed under reduced pressure, and then a polymer emulsion having asolid content of about 40% was obtained. The particle diameter ofpolymer particles dispersed in the emulsion was in the range of about100 nm to about 200 nm, and the average particle diameter was about 120nm.

PREPARATION EXAMPLE 2

After flushing nitrogen in a 10 L autoclave reactor, about 60 parts byweight of distilled water and about 1.5 parts by weight ofdodecylbenzenesulfonic acid sodium salt were then added, and thetemperature was increased to about 70° C. Subsequently, about 2 parts byweight of styrene was added to the reactor and stirred for about 5minutes. Then, about 10 parts by weight of a 2% aqueous solution ofpotassium persulfate was added to the reactor to initiate a reaction.After about 1 hour, a monomer emulsion, which included about 40 parts byweight of butadiene, about 46 parts by weight of styrene, about 10 partsby weight of methyl methacrylate, about 3 parts by weight of itaconicacid, about 1 part by weight of hydroxyethyl acrylate, about 0.5 partsby weight of a dodecylbenzenesulfonic acid sodium salt, and about 40parts by weight of distilled water, was added to the reactor for about 4hours. Simultaneously, about 10 parts by weight of the 2% aqueoussolution of potassium persulfate was added to the reactor for about 3hours. After finishing the addition of the monomer emulsion, thereaction was then further performed for about 3 hours. Then, the reactorwas cooled to 20° C., the residual monomer was removed under reducedpressure, and the polymer emulsion was obtained. The polymerization ratewas about 98.9%. A 5 wt % lithium hydroxide aqueous solution was addedto the polymer emulsion to adjust the pH level to about 7.5, and thus,the solid content of the polymer emulsion was adjusted to about 40%.

Preparation of Binder Composition EXAMPLE 1

Based on the dry weight, about 30 parts by weight of a crosslinkedpolymethyl methacrylate emulsion (EPOSTAR MX030W, Nippon Shokubai,Japan) having an average particle diameter of about 50 nm was added toabout 100 parts by weight of the polymer emulsion (solid content ofabout 40%) prepared in accordance with the Preparation Example 1 andstirred for about 10 minutes to prepare a binder composition.

EXAMPLE 2

A binder composition was prepared in the same manner as in Example 1except that the polymer emulsion prepared in Preparation Example 2 wasused.

EXAMPLE 3

Based on the dry weight, about 30 parts by weight of a crosslinkedpolymethyl methacrylate emulsion (EPOSTAR MX030W, Nippon Shokubai,Japan) having an average particle diameter of about 50 nm was added toabout 100 parts by weight of the polymer emulsion (solid content ofabout 40%) prepared in Preparation Example 2 and stirred for about 10minutes. Then, about 0.2 parts by weight ofγ-glycidoxypropyltrimethoxysilane as a silane coupling agent was addedand stirred for about 20 minutes to prepare a binder composition.

COMPARATIVE EXAMPLE 1

The polymer emulsion prepared in accordance with the Preparation Example1 was used as a binder.

COMPARATIVE EXAMPLE 2

The polymer emulsion prepared in accordance with the Preparation Example2 was used as a binder.

Preparation of Anode and Lithium Battery EXAMPLE 4

An Si—Fe alloy active material (CV3, 3M, St. Paul, Minn., USA) having anaverage particle diameter (d₅₀) of about 3 μm, artificial graphite (MAG,Hitachi Chemical Co., Ltd., Tokyo, Japan), and carboxymethyl cellulose(CMC) were mixed in pure water, and the active material slurry was thenprepared to obtain a weight ratio of Si—Fe alloy:graphite:CMC:binder(solid content) of about 20:77:1:2 by combining with the bindercomposition prepared in Example 1.

A copper foil with an original thickness of about 10 μm was coated withthe active material slurry to a thickness of about 90 μm, and then driedat about 110° C. for about 0.5 hours. Then, an anode plate was preparedby roll-pressing the coated copper foil to a thickness of about 70 μm. Acoin cell (CR2016 type) having a diameter of about 32 mm was prepared.

Metallic lithium was used as a counter electrode for the preparation ofthe coin cell, an about 20 μm thick polyethylene separator (Star 20) wasused as a separator, and an electrolyte used was prepared by dissolvingabout 1.15 M LiPF₆ in a solvent mixture of ethylene carbonate(EC):ethylmethyl carbonate (EMC):diethyl carbonate (DEC) (a volume ratioof about 3:3:4).

EXAMPLE 5

An anode and a lithium battery were prepared in accordance with the sameprocedures described in Example 4 except that the binder compositionprepared in Example 2 was used.

EXAMPLE 6

An anode and a lithium battery were prepared in accordance with the sameprocedures described in Example 4 except that the binder compositionprepared in Example 3 was used.

COMPARATIVE EXAMPLES 3 AND 4

Anodes and lithium batteries were prepared in accordance with the sameprocedures described in Example 4 except that the binder compositionsprepared in Comparative Examples 1 and 2 were respectively used.

EVALUATION EXAMPLE 1 Glass Transition Temperature Test

Substrates were respectively coated with the binder compositions ofExamples 1 to 3 and Comparative Examples 1 and 2, and solvents were thenremoved by drying at room temperature for about 24 hours. Then, bindersamples were respectively prepared by separating films from thesubstrates. Glass transition temperatures of the binder samples weremeasured using a differential scanning calorimeter (DSC).

The glass transition temperature of the binder sample prepared from thebinder composition of Example 1 was about 18° C.

EVALUATION EXAMPLE 2 High-Temperature Elastic Modulus Measurement

Substrates were respectively coated with the binder compositions ofExamples 1 to 3 and Comparative Examples 1 and 2, and solvents were thenremoved by drying at room temperature for about 24 hours. Then, bindersamples were respectively prepared by separating films from thesubstrates.

Changes in strain according to stress tests were measured for the bindersamples using a tensile tester manufactured by Instron Corporationaccording to ASTM standards. Elastic moduli (E) of the binders at 60° C.were calculated from the slopes of stress-strain graphs.

TABLE 1 Elastic Modulus [10⁹ Pa] Example 1 8 Example 2 53 Example 3 27Comparative Example 1 7 Comparative Example 2 2

As illustrated in Table 1, the binders obtained from the bindercompositions of Examples 1 to 3 had increased elastic moduli incomparison to the binders of Comparative Examples 1 and 2.

EVALUATION EXAMPLE 3 Charge and Discharge Characteristics and ElectrodeExpansion Ratio Evaluation

The coin cells prepared in Examples 4 to 6 and Comparative Examples 3and 4 were charged at a 0.2 C constant current rate to a voltage of 0.01V (vs. lithium (Li)) at 25° C. and charged to a current of 0.01 C whilemaintaining a constant voltage of 0.01 V. Subsequently, the coin cellswere discharged at a 0.2 C constant current until the voltage reached1.5 V (vs. Li) during discharging (formation operation).

The lithium batteries subjected to the above formation operation werecharged at a 0.5 C constant current rate to a voltage of 0.01 V (vs. Li)at 25° C. and charged to a current of 0.01 C while maintaining aconstant voltage of 0.01 V. Subsequently, the lithium batteries weredischarged at a 0.5 C constant current until the voltage reached 1.5 V(vs. Li) during discharging, and the above cycle was repeated 30 times.

Some of the results of charge and discharge experiments are presented inTable 2 below. The capacity retention ratio and the electrode expansionratio are defined as the following Equations 1 and 2, respectively.

The electrode expansion ratio was calculated from the following Equation2 by respectively measuring a thickness of an anode before assemblinginto a battery and a thickness of an anode after disassembling thebattery after 30 charge and discharge cycles and then removing theelectrolyte.

Capacity retention ratio [%]=[discharge capacity at a 30thcycle/discharge capacity at the 1st cycle]×100   <Equation 1>

Electrode expansion ratio [%]=[thickness of an anode after 30 charge anddischarge cycles/thickness of an unused anode]×100   <Equation 2>

TABLE 2 Capacity retention ratio in a 30th cycle Example 4 89.4 Example5 90.6 Example 6 90.4 Comparative Example 3 83.7 Comparative Example 483.8

As illustrated in Table 2, the lithium batteries of Examples 4 to 6exhibited increased the battery cycle life characteristics in comparisonto the lithium batteries of Comparative Examples 3 to 4.

Also, the electrode expansion ratios of the lithium batteries ofExamples 4 to 6 were significantly reduced in comparison to electrodeexpansion ratios of the lithium batteries of Comparative Examples 3 to4. For example, the electrode expansion ratios of the lithium batteriesof Examples 4 to 6 were about 40% or less. However, the electrodeexpansion ratios of the lithium batteries of Comparative Examples 3 to 4were about 60% or more.

Therefore, since the electrode expansion ratios of the lithium batteriesof Examples 4 to 6 including the binders having increased strength orelastic modulus were reduced, the battery life characteristics of thelithium batteries were increased.

As described above, the cycle characteristics of a lithium battery maybe increased by including a binder which includes polymethylmethacrylate particles and a binder polymer.

It should be understood that the exemplary embodiments described thereinshould be considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments of the present invention have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thepresent invention as defined by the following claims.

What is claimed is:
 1. A binder for a battery comprising: polymethylmethacrylate particles; and a binder polymer.
 2. The binder for thebattery of claim 1, wherein an average particle diameter of thepolymethyl methacrylate particles is in the range of about 10 nm toabout 200 nm.
 3. The binder for the battery of claim 1, wherein theweight ratio of the polymethyl methacrylate particles to the binderpolymer is in the range of about 100:10 to about 100:60.
 4. The binderfor the battery of claim 1, wherein the binder for the battery has oneor more glass transition temperatures.
 5. The binder for the battery ofclaim 1, wherein the binder for the battery has one or more glasstransition temperatures of about 60° C. or less.
 6. The binder for thebattery of claim 1, wherein the glass transition temperature of thebinder for the battery is in the range of about −50° C. to about 60° C.7. The binder for the battery of claim 1, wherein the polymethylmethacrylate particles in the binder for the battery are crosslinkedpolymethyl methacrylate particles that do not have a glass transitiontemperature.
 8. The binder for the battery of claim 1, furthercomprising a coupling agent.
 9. The binder for the battery of claim 8,wherein the coupling agent is a silane-based compound.
 10. The binderfor the battery of claim 8, wherein the coupling agent is a hydrolysateof a silane coupling agent.
 11. The binder for the battery of claim 10,wherein the silane coupling agent comprises one or more selected fromthe group consisting of an alkoxy group, a halogen group, an aminogroup, a vinyl group, a glycidoxy group, and a hydroxyl group.
 12. Thebinder for the battery of claim 10, wherein the silane coupling agentcomprises one or more selected from the group consisting ofvinylalkylalkoxysilane, epoxyalkylalkoxysilane,mercaptoalkylalkoxysilane, vinylhalosilane, and alkylacyloxysilane. 13.A binder composition for a battery comprising: polymethyl methacrylateparticles; binder polymer particles; and a solvent.
 14. The bindercomposition for the battery of claim 13, wherein the polymethylmethacrylate particles are included in an amount of about 10 parts byweight to about 60 parts by weight based on 100 parts by weight of thebinder polymer particles.
 15. The binder composition for the battery ofclaim 13, wherein an average particle diameter of the polymethylmethacrylate particles is in the range of about 10 nm to about 200 nm.16. The binder composition for a battery of claim 13, wherein an averageparticle diameter of the binder polymer particles is in the range ofabout 50 nm to about 500 nm.
 17. An anode comprising: an anode activematerial; and the binder for the battery of claim
 1. 18. The anode ofclaim 17, comprising the binder for the battery in which polymethylmethacrylate particles are dispersed.
 19. The anode of claim 17, whereinthe anode active material comprises one or more selected from the groupconsisting of silicon (Si), tin (Sn), lead (Pb), germanium (Ge),aluminum (Al), SiO_(x) (0<x≦2), SnO_(y) (0<y≦2), Li₄Ti₅O₁₂, TiO₂,LiTiO₃, and Li₂Ti₃O₇.
 20. The anode of claim 17, wherein the anodeactive material further comprises a carbon-based anode active material.21. A lithium battery using the anode of claim 17.